Magnetic marking and positioning system for unfinished metal bars

ABSTRACT

A permanent invisible magnetic marking and positioning system of cylindrical metal steel rods. To accurately locate the physical midpoint of the rod-to-be-cut, a novel head centering and positioning mechanism automatically sets the midpoint distance for each setup as the length of the finished rod stock is changed. The steel rod that is used to manufacture the U-bolts is inserted lengthwise into a cutoff saw station or machine until it comes in contact with a stop that is set to the desired predetermined length. An automatic centering device positions the magnetizing heads located at the longitudinal center, on each side, of the steel rod. A high-energy rectangular pulse imparts a permanent invisible magnetic mark at the longitudinal center of the steel rod before being formed into a U-bolt. The rod is then suitably cut to the desired predetermined length, and each of the opposite ends threaded with the desired thread size. The unbent threaded rod is positioned in the hydraulic or powered bending machine, so that the longitudinal center of the rod is aligned to the center of the bending mandrel, using a peak magnetic detector that is used to locate the magnetic center of the rod. The centering indicator having peak magnetic strength detection allows manual or automatic positioning of the rod so that the center of the magnetic mark is perfectly aligned with the center of the bending mandrel. Once the midpoint of the rod is positioned and aligned with the center of the mandrel, the straight threaded rod is formed into a U-bolt. The magnetic mark remains permanently embedded at the crest of the formed U-bolt, thereby rendering a permanent tag identifying the origin of the U-bolt.

FIELD OF THE INVENTION

The present invention relates primarily to a permanent magnetic marking and positioning system of unfinished metal bars, and more particularly, to a magnetic marking and positioning system, which permits central alignment of a cylindrical steel rod to its longitudinal center or balance point prior to forming in a bending jig.

BACKGROUND OF THE INVENTION

In the manufacture of U-bolts and other related parts, it is common to cut a long steel rod into shorter sections of predetermined length. While each rod section remains straight, each is threaded along the opposite end portions. To produce a U-bolt, each of the threaded straight rods are then successively inserted into a hydraulic or powered bending and forming machine that cold forms each rod around a U-shaped mandrel.

Before performing the bending operation, an operator must place the unbent rod in the bending machine and position it using a tape measure to position it so that the midpoint of the rod is aligned with the center of the mandrel.

When rods of different lengths are being successively formed into U-bolts, it is necessary to readjust the adjustable stops for each rod that is different in length. This requires additional setup time for each group of rods being formed. Still more time is wasted in determining the longitudinal center of the rod, and then positioning it over the center of the mandrel. This manual process is also subject to human operator error due to fatigue.

Visual marking and forming machines used for the production of U-bolts is well known in the prior art. Disclosed are several forming machines that use a variety of longitudinal center marking methods. Examples of such prior art are shown in the patents that follow.

U.S. Pat. No. 4,835,805, granted Jun. 6, 1989, to J. C. Gray, discloses the production of threaded metal rods for making U-bolts, where straight cylindrical metal rods are threaded along opposite ends and the center portion is marked to form a visual indicator of the longitudinal center of the rod. The mark identifying the center of each rod extends circumferentially around the metal rod and is formed by a stripe of color contrasting ink directly to the rod provide a permanent mark that does not require rotating the rod to find the mark. The mid-point mark on each rod is aligned with the center plane mark on the machine and the rod is bent to form a precision U-bolt.

U.S. Pat. No. 4,654,912, granted Apr. 7, 1987, to J. C. Gray, discloses the production of threaded metal rods for making U-bolts, where straight cylindrical metal rods are threaded along opposite ends and the center portion is marked to form a visual indicator of the longitudinal center of the rod. The mark identifying the center of each rod extends circumferentially around the metal rod and is formed by a stripe of color contrasting ink to provide a permanent mark that does not require rotating the rod to find the mark. The mid-point mark on each rod is aligned with the center plane mark on the machine and the rod is bent to form a precision U-bolt.

U.S. Pat. No. 4,572,293, granted Feb. 25, 1986, to J. G. Wilson, et al., discloses a method for placing magnetic markers on collarless cased wellbores. A magnetic marker is used to locate wireline tools in wellbores using collarless housing. The magnetic marker is applied at selected positions on the casing before or after placing casing in a well.

U.S. Pat. No. 4,446,711, issued to Raymond L. Valente on May 8, 1984, discloses and claims a novel improvement for a U-bold bender.

Still another prior art patent, U.S. Pat. No. 4,572,293, issued to Wilson, et al., on Feb. 25, 1986, discloses the use of magnetic depth markers placed at regular vertical intervals for depth of wireline tools during a logging run.

The prior art recited above does not teach of the novel advantages that are found in the present invention. Several teach of using visual stripes using tapes or labels to mark the center of the rod being formed.

Accordingly, it is therefore an object of the present invention to provide a novel positioning means to locate the longitudinal center of a cylindrical steel rod prior to being cut to a desired predetermined length.

It is another object of the present invention to provide a novel magnetic marking means at the longitudinal center of a cylindrical steel rod prior to being cut to a desired predetermined length.

It is still another object of the present invention to provide a novel positioning and longitudinal centering means for a magnetically marked cylindrical steel rod so that it can be formed into a precise U-bolt, having equal and symmetrical ends.

A final object of the present invention is to provide a novel method of marking a cylindrical steel rod, using a permanent non-visual marker, to provide a coded identification of the manufacturer in the event of a catastrophic failure of the entire assembly, such as in an aircraft failure.

These as well as other objects and advantages of the present invention will be better understood and appreciated upon reading the following detailed description of the preferred embodiment when taken in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

The present invention relates primarily to a novel permanent magnetic marking and positioning system of unfinished metal bars, which aligns a cylindrical ferrous rod to its longitudinal center point (or balance point) prior to forming in a bending and forming machine.

In one aspect of the present invention, the ferrous rod that is used to manufacture the U-bolts is magnetically marked at its center-point and then cut to the desired length by longitudinally inserting the raw cylindrical rod into a cutoff saw station or machine until it comes in contact with a stop that is set to the desired predetermined length. The frame includes at least one magnetizing head each including an electromagnetic coil. An automatic centering device positions each magnetizing head located at the longitudinal center, on each side, of the rod. While positioned at a midpoint of a secured rod a high energy current pulse is provided across the coil to the rod, thereby magnetically marking the midpoint of the rod with a permanent invisible magnetic mark indicator of a longitudinal center of the rod.

The system is automated, for when the raw cylindrical rod comes in contact with the stop, it closes a switch which results in sending a high energy current pulse to an electromagnetic coil mounted on each magnetizing head, thereby magnetically marking the midpoint of the steel rod prior to being cut to the desired predetermined length. Typically, the pulse is rectangular, having an amplitude in the range of 10 to 50 volts, preferably 24 volts and a duration in the range 10 to 500 milliseconds, preferably at least 100 milliseconds.

After each magnetically marked rod is suitably cut to the desired predetermined length, each of the opposite ends is threaded to the desired thread size.

In another aspect of the present invention, the unbent threaded steel rod is positioned in the hydraulic or powered bending machine, so that the longitudinal center of the rod is aligned to the center of the bending mandrel. A peak magnetic detector is used to locate the magnetic center of the rod. The peak detector gives a visible presentation on a meter, in either digital or in analog form, or even gives an audible ‘beep’ at the located midpoint. A centering indicator having peak magnetic strength detection allows manual or automatic positioning of the rod so that the center of the magnetic mark is perfectly aligned with the center of the bending mandrel. Once the midpoint of the rod is positioned and aligned with the center of the mandrel, the straight threaded rod is formed into a U-bolt.

The magnetic mark remains permanently embedded at the crest of the formed U-bolt, thereby rendering a permanent tag identifying the origin of the U-bolt.

As such, the invention comprises a system for locating and marking a midpoint of unfinished rod stock placed on a support frame, table, workbench or cutoff station, with a means for securing a rod in a fixed position, a means for locating a longitudinal center of the rod before being cut to length and, a means for embedding in the rod a permanent invisible indicator of the longitudinal center of the rod. The frame includes a repositioning end stop for receiving rods of varying lengths, the end stop having an associated microswitch actuated by contact with a rod inserted on the frame and communicating with a grip, for closure of grip to automatically secure the rod in the desired position for marking a midpoint of a specified rod length.

When in use, the invention provides a method of efficiently producing heavy duty U-bolts of different sizes, wherein each U-bolt has two legs of substantially equal length. The method includes the steps of providing a supply of straight metal rods with opposite ends, smooth cylindrical outer surfaces, different predetermined lengths, and transverse center planes defining a longitudinal center of each rod substantially equidistant from the ends of each rod. Helical threads are formed on opposite end portions of each rod, which are successively fed into a marking machine having an at least one relative movable magnetizing head with means for embedding an invisible magnetic mark center indicator to the rods. The rods are successively marked by imparting a current pulse from an electromagnetic coil at substantially the transverse center plane of each rod to produce a permanent invisible magnetic mark center indicator at the longitudinal center of each rod, whereupon the rods are successively transferred from the marking machine and inserted into a forming machine with a mandrel for bending.

The rods are supported between two mandrel bending members which are relatively movable with respect to each other, the mandrel having a magnetic detector, a mandrel center mark, and a surface for supporting the rod between its ends during bending. Each rod is positioned with the embedded magnetic mark center indicator in alignment with the mandrel center mark by use of the magnetic detector, succeeded by moving the mandrel and the bending members with respect to each other to bend each rod around the mandrel surface. The bending members engage the rod in an area spaced longitudinally from the permanent invisible magnetic mark center indicator of each rod. In this manner, a U-bolt having two legs of substantially equal length is produced from each rod for providing a supply of U-bolts differing in leg length size from each other with minimum scrap resulting from differing leg lengths in a single U-bolt.

In an alternative embodiment, the magnetic mark is made using two magnetizing heads on either side of the cylindrical rod, where the first head imparts a magnetic north imprint and the second head, a magnetic south imprint. By using a double magnetic imprint, a discriminator circuit is used to locate the magnetic center, which with correct calibration, coincides with the midpoint of the rod.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is pictorially illustrated in the accompanying drawings that are attached herein.

FIG. 1 is a perspective view of a straight cylindrical steel rod, positioned at the stop, where the magnetizing heads are positioned at the midpoint of the rod, prior to being cut to the desired specified length.

FIG. 2 is a plan view of the novel dual midpoint locating device as applied to the cutoff station.

FIG. 3 is an exploded side view of the magnetizing head inward positioning arrangement.

FIG. 3A is a side elevation of the magnetizing head inward positioning arrangement having a motorized drive to position the pulse marking magnetizing head.

FIG. 3B is a schematic drawing showing the detailed electrical connections to the DC motor for the motor reversal sequences to position and retract the magnetizing heads.

FIG. 4 is a sectional view of the magnetizing head inward positioning arrangement.

FIG. 5 is a plan view of an alternative embodiment showing a single magnetizing head positioned at the midpoint of the rod as applied to the cutoff station.

FIG. 6 is a perspective view of a straight metal rod having opposite threaded end portions and a center portion with a permanent magnetized mark indicating the midpoint of the rod as located and embedded pursuant to the present invention.

FIG. 7 is a side elevational view of one form of a manual rod bending-machine used to form a U-bolt having a magnetic sensing head to determine the location of the magnetic mark.

FIG. 7A is a block diagram that illustrates the magnetic mark pickup head, connected to a preamplifier, whose output is an analog meter that shows the meter deflection being proportional to the intensity of the magnetic mark.

FIG. 8 is a side elevational view of a U-bolt formed from a rod as illustrated in FIG. 1.

FIG. 9A is an exploded view of the magnetic mark imparted by two magnetizing heads, each of opposite polarity, on the same side of the cylindrical rod.

FIG. 9B details the corresponding electrical discriminator output with reference to the magnetically marked cylindrical rod as shown in FIG. 9A.

FIG. 10 is a side elevational view of an alternative embodiment having one form of a manual rod bending-machine used to form a U-bolt using a compass-like visual indicator to determine the location of the magnetic mark.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, the cylindrical metal rod 10 is shown being cut to the desired length, from the metal rod stock 15. The rod stock 15, stabilized on a table, workbench or support frame 17, is inserted longitudinally into the cutoff station until it reaches the end stop 20. Two magnetizing heads 30 a and 30 b, each bearing a coil 30, are placed on either side of the inserted cylindrical rod stock 15 at its midpoint, where it is magnetically marked by passing a momentary pulse of DC current through the coil of the magnetizing heads. Upon completion of magnetically marking the longitudinal center of the metal rod, it is cut to the desired length using cutoff saw 25.

The straight metal rod 10 is commonly manufactured in a wide range of diameters that range from ¼ inch to 1¼ inches. Depending upon the application, the material composition that is used for the U-bolts can be of a mild steel.

To provide an automated means of finding the midpoint of the cylindrical rod portion 10, before it is cut to length, a novel dual head positioning linkage 35 mounted upon the cutoff station base 26 is shown in FIG. 2.

The end stop 20 is positioned in the cutoff station by sliding it along the track openings 45, then securing it when the desired position is reached. The metal rod stock 15 is inserted into the cutoff station until it comes in contact with end stop 20, where it actuates microswitch 40. Upon the closure of microswitch 40, the grip or rod-clamps 100 grip the uncut cylindrical rod stock 15 maintaining it securely in position. With the uncut rod 15 being held securely in position, a short high energy current pulse energizes the magnetizing heads 30 a and 30 b to invisibly mark the midpoint of the rod before it is cut to its final length. The rod is then cut to length along the section designated as 105.

As illustrated, the upper portion of the head positioning and centering linkage apparatus is comprised of equal arms 50 a and 55 a, and telescoping arms 90 a and 95 a, which form an equilateral triangle. Bisecting center arm 150 a subdivides the angle formed by arms 50 a and 55 a, by virtue of the fact, that arm 155 a is parallel to arm section 165 a, and arm 160 a being parallel to arm section 170 a, thereby forming a parallelogram while maintaining arm 150 a precisely directed toward the midpoint of the rod being cut off. The head 30 a, being firmly attached to arm 150 a, moves in a path that is parallel to rod 15, by virtue of the follower guide pin 110 a traversing through the slotted channels 115 a and 120 a found in telescoping arms 90 a and 95 a, which form the base of the triangle. By maintaining the accuracy of the arms, with respect to the distances between pivots 60 a, 65 a, 70 a, 75 a, 80 a and 85 a, the center arm bisects an angle between the equal arms 50 a and 55 a and bisects the telescoping base 90 a-95 a. The magnetizing heads 30 a and 30 b will always be positioned at the midpoint of the rod being prepared for use, independent of the change in tooling setup for different U-bolts, having varying lengths and diameters. Additionally, to preserve the setup accuracy, it is necessary that the horizontal distance between the saw cut 105 and the pivot 60 a be equal to the horizontal distance between the inner surface of end stop 20 and the pivot 65 a.

The lower portion of the head positioning and centering apparatus is an identical mirror image of the left side portion where all numerical designators are suffixed with the letter ‘b’.

Turning now to FIGS. 3 and 4, there is shown in detail, the head extension apparatus. The coil 30 of a magnetizing head 30 a, 30 b is mounted to the slide carriage 125, having a truncated triangular cross-section that traverses its mating receiving channel 130 in slide base 135. The entire slide apparatus is mounted orthogonal to the rod 15. Also attached to the slide carriage 125 is an adjustor receptacle 140 that captivates the ball end 145 of the head adjustment screw shaft 150. The base 135 is rigidly mounted on top of the arm 80, and the follower guide pin 110 is attached below to the bottom of arm 80.

In a first alternative embodiment, as shown in FIGS. 3A and 3B, the orthogonal head positioning assembly may be motorized to enable the heads to be retracted when the uncut rod is inserted into the cutoff station. When the rod reaches the end stop, the microswitch 230 is actuated and the heads 30 a and 30 b are restored to their operating positions.

In typical operation, with no rod in the cutoff station, the magnetizing heads 30 a and 30 b are in their fully retracted outward position. When an uncut rod 15 is inserted into the cutoff station, the rod is positioned forward toward the stop 20 until it depresses the rod position-sensing switch 230. Upon actuation of switch 230, the relay 235 becomes energized, causing its relay contacts to close, which results in the reversible motor, preferably a DC motor 190 to rotate in a clockwise direction. Mounted to the shaft of the DC motor 190 is a pinion assembly 200, with a small pinion (not shown) engaged with the larger pinion 200 to cause the screw shaft 150 to rotate in a counterclockwise direction. The screw shaft 150, being screwed into the threaded head adjustor receptacle 142, causes the magnetic heads 30 a and 30 b to move inwardly, via carriage 125, toward the uncut rod 15. When the head adjustor receptacle 142 comes in contact with forward adjustable travel limit switch 225, it actuates the switch causes the motor 190 to stop its rotation. The switch 225 is suitably mounted so that it can be adjusted for the varying diameters of rods during the setup procedure.

After the magnetizing pulse is imparted into the metal rod 15, the rod is cut to the desired length 10 in the saw cut region 105. Upon completion of the saw cut, the cut rod 10 drops releasing its contact with rod sensing switch 230, causing the motor 190 to start rotating in the reverse direction. Concurrently, the rod clamp jaws 100 are subsequently disengaged releasing the clamped rod 15. The motor 190 continues rotating in the same direction until it contacts travel limit switch 220, which opens the switch contacts, resulting in the motor to stop its rotation. The magnetizing heads 30 a and 30 b now have been moved into their fully retracted position, allowing the uncut rod to be inserted without causing damage to the heads, which completes the cycle for this operation.

In a second alternative embodiment, FIG. 5 illustrates a single magnetizing head centering and positioning mechanism that may be used when the rod diameters are of reduced size. The single head positioning and centering apparatus 36 is identical to the upper linkages as shown in FIG. 2, where all of the numerical designators are suffixed with the letter ‘a’.

FIG. 6 illustrates the cylindrical steel rod 10 after being first receiving the invisible magnetic mark 155, subsequently cut to the desired length, and then in an ensuing operation, having both ends receiving threaded portions 160.

FIG. 7 illustrates a manual U-bolt bending machine 165 adapted to receive a magnetic mark pickup head 180 to detect the magnitude of the recorded magnetic midpoint mark. The output of the pickup head 180 is amplified, then displayed on a meter connected to the amplifier output. As the rod 10 is moved to the left, as shown, the meter deflects to a maximum indicating a maximum peak that coincides with the midpoint of the rod 10. When the magnetic mark coincides with the center alignment mark of the mandrel 175, the bending of the rod 10 to form a U-bolt may commence.

There is shown in FIG. 7A, a block diagram that illustrates the magnetic mark pickup head 180, connected to preamplifier 205, whose output is an analog meter 210 that shows the meter deflection being proportional to the intensity of the magnetic mark. It may be advantageous to provide alternatively a digital numeric readout 240 to give the operator a more precise readout of the imprinted magnetic mark. In still another embodiment, a speaker 245 connects to the amplifier output to provide an audible output that is proportional to the magnetic intensity, thereby enabling the operator to manually position the rod without having to observe a panel meter readout.

FIG. 8 shows a finished manufactured U-bolt 185, after being formed in the U-bolt bending machine, having the invisible magnetic mark 155.

FIGS. 9A and 9B illustrate another embodiment, where the magnetic mark is made by having two magnetizing heads 32 a and 34 a, of opposite polarity, placed next to each other on the same side of the cylindrical rod. The first head 32 a imparts a magnetic north imprint and the second head 34 a, a magnetic south imprint. With a double magnetic imprint, with each having a comparable magnetic strength, a discriminator circuit is used to locate the magnetic center, (a zero crossing as displayed on a galvanometer), which with correct calibration, coincides with the midpoint of the rod. The midpoint is precisely where the output of the discriminator output crosses zero.

With reference now to FIG. 10, still another embodiment is illustrated where a simple magnetic indicator is used to locate and display the magnetic center mark imparted to the steel rod. The magnetic indicator is similar to that of a direction finding compass where instead of pointing to the earth's magnetic north, the indicator points toward the midpoint of the invisible permanent magnetic mark.

It should be understood that there may be numerous modifications, advances or changes that can be made to the present invention, but in doing so, it is intended that they should not detract from the true spirit of the present invention. 

We claim:
 1. A system for locating and marking a midpoint of unfinished rod stock, comprising: a support frame with a means for securing a rod in a fixed position, a means for locating a longitudinal center of the rod, and a means for embedding in the rod a permanent invisible indicator at the longitudinal center of the rod.
 2. The system of claim 1, the frame including a repositioning end stop for receiving rods of varying lengths, wherein the end stop is temporarily fixed at a specified rod length for marking a longitudinal center of the specified rod length.
 3. The system of claim 2, the frame including an at least one magnetizing head having an electromagnetic coil positioned at the longitudinal center of the rod, wherein a current pulse across said coil to the center of the rod embeds in the rod the invisible indicator comprising a magnetic mark center indicator of the longitudinal center of the rod.
 4. The system of claim 3, wherein the rod is magnetically marked at the longitudinal center of a specified length of rod prior to being cut to the specified length.
 5. The system of claim 4, the frame further comprising a head positioning linkage that includes a pair of pivotally joined sides of equal length and each side also pivotally joined to an end of a telescoping base, the sides and base shaped as an expansible equilateral triangle, whereby the linkage can accommodate variously sized unfinished rod stock positioned parallel to said base.
 6. The system of claim 5, each at least one magnetizing head mounted on a center arm of the linkage that bisects the angle between the sides and further bisects the base, the center arm slidably mounted on the triangle and directed by a pair of guide arms, each guide arm pivotally joined to said center arm and to a respective triangle side, wherein the guide arms direct the center arm which precisely locates the magnetizing head at the longitudinal center of the rod on the frame, to embed the magnetic mark center indicator at said rod center, independent of the length or diameter of the rod inserted on the frame.
 7. The system of claim 6, wherein each magnetizing head is mounted to a slide carriage captivated in a channel of a slide base that is fixed on top of the center arm, with a head adjustment screw on the base having a ball end retained in an adjuster receptacle on the carriage, to advance and retract each magnetizing head to an optimum distance from the rod.
 8. The system of claim 7, further comprising a follower guide pin attached to a bottom portion of the center arm and inserted into a slotted channel grooved through a pair of opposed arms that form the triangle telescoping base, whereby each magnetizing head moves in a path parallel to a longitudinal axis of the rod with the coil constantly orthogonal to the rod.
 9. The system of claim 8, the at least one magnetizing head comprising a pair of magnetizing heads each located on an opposite side of the rod and mounted on identical head positioning linkages and fixed to identical center arms, such that each magnetizing head is directed to the center of the rod for magnetic marking at said center.
 10. The system of claim 8, the at least one magnetizing head comprising two adjacent magnetizing heads of opposite polarity fixed on a center arm and positioned on a same side of the rod, which impart a first magnetic imprint and a second magnetic imprint of opposite polarity to the rod.
 11. The system of claim 8, the frame comprising a cutoff station including a saw for cutting a magnetically marked rod to a specified length, wherein a horizontal distance between a rod cut-off point and a pivot that joins a first side and the base of the triangle is essentially equal to a horizontal distance between an inner surface of the end stop and a pivot that joins the second side to the base, for preserving a setup accuracy.
 12. The system of claim 11, further comprising a bending machine with a mandrel including a means for detecting the rod magnetic mark center indicator for alignment of the rod with a mandrel center mark to bend the rod on the mandrel for forming a U-bolt with parallel, symmetric ends.
 13. The system of claim 12, the means for detecting comprising a peak magnetic detector.
 14. The system of claim 13, wherein the rod magnetic midpoint is located using a simple magnetic indicator for centering the rod on the mandrel for bending.
 15. The system according to claim 13, the peak magnetic detector comprising a discriminator circuit including a galvanometer, wherein a discriminator output which is displayed as a zero crossing on the galvanometer, coincides with the midpoint of the rod.
 16. The system of claim 15, wherein the invisible magnetic mark center indicator is embedded at a crest of the U-bolt and includes a coded identification tag, for identifying a manufacturer of the U-bolt.
 17. The system of claim 16, wherein the pulse comprises a rectangular pulse with an amplitude in a range from about 10 volts to about 50 volts.
 18. The system of claim 17, the pulse having a duration of about 10 milliseconds to about 500 milliseconds.
 19. The system of claim 18, the pulse preferably comprising a duration of at least 100 milliseconds.
 20. The system of claim 16, wherein the invisible magnetic mark center indicator is embedded at a crest of the U-bolt and includes a coded identification tag, for identifying a manufacturer of the U-bolt.
 21. A magnetic marking and positioning system for use in making U-bolts, comprising: a cutoff station including a centering linkage with a means for locating a longitudinal center of a specified rod length prior to cutting the rod to the specified length; a circuit actuated by placing the rod on the station, connected to a means for securing the rod on the station and a means for sending an electromagnetic pulse to the rod, said means for sending positioned at the rod center using the means for locating; and, means for opening the circuit concurrent with a release of the rod when the rod is cut to the specified length.
 22. The magnetic marking and positioning system of claim 21, the linkage further comprising a bisecting arm that locates a longitudinal center of a rod, an at least one magnetizing head each having an electromagnetic coil connected to the linkage bisecting arm and to the circuit having a reversible motor, an end stop on the station with a microswitch actuated by contact with a rod inserted on the station for closure of a station grip to secure the rod, a concurrent motor rotation that drives an adjustment screw, via a pinion assembly, which advances each head to an operating position at the rod center, a coil pulse registry of a permanent invisible magnetic mark center indicator at the longitudinal center of the rod, and an automatic retraction of each head upon a cut of the rod that drops from the station with release of the rod contact with the microswitch, by a motor reversal that moves each magnetizing head to a fully retracted position.
 23. The magnetic marking and positioning system of claim 22, the circuit further comprising a means for limiting the advance of each magnetizing head toward the rod.
 24. The magnetic marking and positioning system of claim 23, the circuit further comprising a means for limiting the retraction of each magnetizing head.
 25. A rod having an invisible indicator of a longitudinal center of the rod for positioning the rod in a process for bending the rod into a U-bolt with equal, parallel ends, said permanent invisible indicator formed, by the steps of: a. securing a rod in a fixed position on a cutting station; b. locating a longitudinal center of a specified rod length; and, c. embedding in the rod the permanent invisible magnetic mark indicator of the longitudinal center of the rod.
 26. The rod according to claim 25, formed by the additional step of: d. cutting the rod to the specified length.
 27. The rod according to claim 26, wherein the cutting station includes an automated means for locating the longitudinal center of the rod including an at least one magnetizing head each having an electromagnetic coil positioned at the rod center by the locating means.
 28. The rod according to claim 27, wherein c., the embedding in the rod step, includes: e. passing a current pulse from the coil to the rod for embedding the magnetic mark.
 29. The rod according to 28, including the additional steps of: f. placing the rod in a bending machine containing a mandrel with a center mark and an associated magnetic pickup head connected to a preamplifier; g. positioning the rod on the mandrel at a peak point registered by the detector, whereby the rod is centered on the mandrel center mark; and, h. activating the bending machine to form the U-bolt with equal, parallel ends.
 30. The rod according to claim 29, the pickup head preamplifier having an output to show a detected magnitude of the magnetic center mark.
 31. The rod according to claim 30, the pickup head preamplifier output comprising an analog meter.
 32. The rod according to claim 30, the pickup head preamplifier output comprising a digital numeric readout to provide a more precise positioning of the magnetic mark.
 33. The rod according to claim 30, wherein the pickup head preamplifier is connected to a speaker which provides an audible output proportional to the magnetic intensity, whereby an operator manually positions the rod without having to observe a panel meter readout.
 34. A method for making a U-bolt, comprising the steps of: a. placing an unfinished rod stock on a cutoff station having a center locating linkage with a bisecting arm bearing an at least one magnetizing head each head having an electromagnetic coil; b. locating a longitudinal center of the rod using the center locating linkage; c. inputting an electromagnetic pulse to the coil and the rod to create a permanent invisible magnetic mark center indicator in the rod at said longitudinal center of the rod; d. positioning the rod center point at a center mark of a bending machine mandrel using a magnetic detector; and, e. bending the rod to form a U-bolt wherein the invisible magnetic mark center indicator is embedded at a crest of the U-bolt.
 35. The method for making a U-bolt of claim 34, wherein the invisible magnetic mark center indicator embedded at the crest of the U-bolt includes a coded identification tag for identifying a manufacturer of the U-bolt.
 36. The method for making a U-bold according to claim 35, wherein the locating linkage comprises an expansible equilateral triangle having a telescoping base and a center arm directed by guide arms to a longitudinal center of the rod.
 37. A method of efficiently producing heavy duty U-bolts of different sizes, wherein each U-bolt has two legs of substantially equal length, the method comprising the steps of providing a supply of straight metal rods, the rods having opposite ends, smooth cylindrical outer surfaces, different predetermined lengths, and transverse center planes defining a longitudinal center of each rod substantially equidistant from the ends of each rod, forming helical threads on opposite end portions of each rod, successively feeding the straight metal rods into a marking machine having an at least one relative movable magnetizing head with means for embedding an invisible magnetic mark center indicator to the rods, successively marking the rods by imparting a current pulse from an electromagnetic coil at substantially the transverse center plane of each rod to produce a permanent invisible magnetic mark center indicator at the longitudinal center of each rod, successively transferring the rods from the marking machine, inserting each rod for bending into a forming machine having a mandrel supported between two bending members, said mandrel and said bending members being relatively movable with respect to each other, the mandrel having a magnetic detector, a mandrel center mark, and a surface for supporting the rod between its ends during bending, positioning each rod with the embedded magnetic mark center indicator in alignment with the mandrel center mark using the magnetic detector, and moving the mandrel and the bending members with respect to each other to bend each rod around the mandrel surface, with the bending members engaging the rod in an area spaced longitudinally from the permanent invisible magnetic mark center indicator of each rod, thereby producing a U-bolt having two legs of substantially equal length from each rod and a supply of U-bolts differing in leg length size from each other, and with minimum scrap resulting from differing leg lengths in a single U-bolt. 